1. Field of the Invention
This invention relates to a one-part or a multipart plastic closure for fastening to the neck of a flexible bottle for dispensing thixotropic fluids, having a bottom part with a circumference wall and a top surface into which a pouring opening is formed.
2. Discussion of Related Art
Thixotropic fluids are fluids with a non-Newtonian flow behavior. A typical example of such a fluid is ketchup. Various liquid soaps also exhibit thixotropic behavior, as do many dispersions. Today, such fluids are sold in flexible plastic containers having closures with a so-called closure membrane. There are many known embodiments of closures with a so-called closure membrane. Examples include those taught by European Patent References EP-A-545 678 and EP-A-442 379, and also U.S. Pat. No. 2,175,052. The significant advantage of closures having a closure membrane is that the already open container can be stood on its head without the fluid leaking out of it. Pressure exerted on the flexible bottle deforms the closure membrane, as described in PCT International Application WO 2006/11915, or the usually slit-shaped opening spreads open and the fluid can be squeezed out of the bottle, as described in the above-mentioned documents. In this case, one problem arises if the membrane is tautly held, for a better closing force and the quicker the closure closes when the pressure on the container is released. As a result, an ever more powerful vacuum builds up in the container over time so that the bottle becomes more and more deformed as its contents are consumed and also the pressure required to dispense the fluid is increased. If the closure membrane is stretched less tautly, then at least sometimes, a certain amount of the displaced air can flow back into the container. Thus, the closure also tends to drip. Furthermore, the more tautly the closure membrane is stretched, the more the closure tends to open explosively when pressure is exerted, causing a jet to emerge at high velocity and the container to have a tendency to spray.
In order to reduce this problem, a variety of complex known closure membrane closures have a design of the closure membrane which is more and more complex and the very small component requires more and more effort to install it in the closure. With these complex closure membranes, it is possible to produce a closing action and an opening of the slit-shaped closure as soon as a pressure difference exists between the atmosphere and the internal pressure of the bottle. This possibility assures the venting of plastic bottles. But because of the variety of materials that must be used in these plastic bottles with closure membranes, such as the membrane must usually be made of a silicone rubber and the actual closure must be produced from a polypropylene, it is not possible to produce them in one injection procedure in the same machine. Also, the silicone rubber part is a relatively expensive part and for this reason alone, it is desirable for it to be as small as possible. When this part is small, however, and is at the same time highly flexible, its installation by machine is extremely complex and malfunction-prone.
The plastic closures mentioned here, which have closure membranes, are known, for example, from European Patent Reference EP 1 216 932 or German Patent Reference DE-A-196 406 29. Closures of this kind are suitable not only for thixotropic fluids, but also for practically all fluids, with the exception of very low-viscosity fluids or carbonated fluids. Development of the closure according to this invention is for providing a closure that avoids the above-mentioned disadvantages, but is simultaneously limited to the use of thixotropic fluids. Thixotropy is understood as the property of a non-Newtonian fluid in which the viscosity decreases in response to constant shear stress over a certain period of time. After the shear stress stops, the initial viscosity is reestablished. In other words, the longer a thixotropic fluid is moved, the lower its viscosity becomes. Normally, the faster the movement is carried out, the faster the viscosity decreases. In other words, in such a closure, the flow-through direction is changed and the flow is accelerated, thus achieving a good flow capacity of the thixotropic fluid while at the same time, a simple shut-off in the flow direction suffices to prevent leakage at a lower viscosity. This invention makes use of this knowledge, creating a plastic closure that is extremely economical, simple to manufacture and assemble, and that can even be manufactured in one piece.